Cayman/997 engines

[blue72s]

As you may know, with the exception of GT3, all Cayman and 997 engines have a bottom end that is not so good. Seal problem at the rear end; integrated semi dry sump; etc.

If a customer gave you a job to change the bottom end of his engine - say Cayman, what would you do?

TIA

[kenikh]

I'd drop in a GT3 mill.

[Steve@Rennsport]

Interesting question that requires some clarification,...

Given that the only transmissions that can bolt up to these engines are the 996-997-Boxster-Cayman ones, what would be the purpose to change the bottom end (short block)?

Improved durability?

Repair or overhaul?

If you were trying to do something different in a Cayman, your only choices would be something like the X-51 3.8 engine with the Cayman gearbox, or an outright replacement with a GT-3 engine AND transmission (mounted upside down). The latter option would not be easy to do.

[blue72s]

I'd drop in a GT3 mill.
What is a mill?


what would be the purpose to change the bottom end (short block)?

Improved durability?

Repair or overhaul?

Improved durability. For tracking/racing (8,000rpm). Also, I'd want dry sump.


If you were trying to do something different in a Cayman, your only choices would be something like the X-51 3.8 engine with the Cayman gearbox, or an outright replacement with a GT-3 engine AND transmission (mounted upside down). The latter option would not be easy to do.
Wow, I had no idea about this. I thought a GT3 engine can bolt up to a Cayman gearbox.. Thanks for this.

[kenikh]

"Mill" means "Motor".

As far as bottom ends go, I am not even sure that the bottom ends on the water cooled cars are swappable. The GT3/GT2 motors are based on modified air cooled cases with water cooled top ends. I am not sure that the top end of a Cayman/996/997 would even bolt onto a GT3 bottom end.

[blue72s]

Can't an adapter be made to make the 6-speed Cayman gearbox to bolt up to a GT3 engine?

What is the difference between the Cayman gearbox and the GT3 gearbox?

[Steve@Rennsport]

FYI,....The 996-997-Cayman-Boxster engines have NOTHING at all in common with the GT-3-GT-2-996TT-997TT engines.

Two totally different and separate engine families.

Same for the transmissions used in these various cars; they are totally different.

Nothing is interchangable so if one chooses an engine from one family, you MUST use the corresponding transmission. A custom adapter could be made, but that creates positioning issues for many components and the GT-3 transmission must still be converted for upsidedown operation.

Personally speaking, I'd not go to all the trouble unless I was going to use the GT-3 engine.

[blue72s]

Why does the GT3 transmission have to be turned upside down?

[Steve@Rennsport]

Originally posted by blue72s
Why does the GT3 transmission have to be turned upside down?

Because it turns the wrong direction for a mid-engined car and the ring gear cannot be moved to the other side,...

[Wayne 962]

I would just buy a GT3 - they are about $80K these days. 996 Turbos can be had for $65K!

-Wayne

[blue72s]

Originally posted by Steve@Rennsport
Because it turns the wrong direction for a mid-engined car and the ring gear cannot be moved to the other side,...

Whoops. Thanks.

Did 914/6 had to do the same with the 915 transmission by turning it upside down?

[Steve@Rennsport]

Originally posted by blue72s
Whoops. Thanks.

Did 914/6 had to do the same with the 915 transmission by turning it upside down?

Nossir,..there is room inside the 915's final drive case to swap the ring gear to the other side.

All of the G-50's must be turned upside down and the oiling system modified to suit with a pump & cooler.

[blue72s]

All of the G-50's must be turned upside down and the oiling system modified to suit with a pump & cooler.

How about a custom ring gear & pinion (from a race transmission manufacturer), identical to the original r&p but in opposite direction? Would this work?

[Steve@Rennsport]

How about a custom ring gear & pinion (from a race transmission manufacturer), identical to the original r&p but in opposite direction? Would this work? [/B]

I really think you'll need a matched pinion shaft to make that durable. I've never had any long-term luck using mis-matched R&P's in these cars as Porsche goes to great measures to match each & every ring & pinion gear to each other for lowest noise and maximum durability.

The R&P are THE most stressed parts of Porsche gearboxes due to the extreme hypoid angle on these parts and the shearing moments experienced by these two parts. Neither lasts very long when you use mis-matched components.

[JohnJL]

Local race-fabrication shop did a 90-minute walkthru of their GT3/Boxster amalgamation at the last PCNSW meeting. In the end, it had more GT3 parts than Boxster. THe owner was happy, but both owner and shop admitted there was more GT3 and it wasn't very cost effective.

They did indeed flop the transmission, and there was diffuiculty fabbing the bellhousing and suspension bits. Also, the GT3 engine needs all the supporting electronics, so in fact the dash instruments were also GT3.

Very cool project tho.

[blue72s]

Originally posted by JohnJL
Local race-fabrication shop did a 90-minute walkthru of their GT3/Boxster amalgamation at the last PCNSW meeting. In the end, it had more GT3 parts than Boxster. THe owner was happy, but both owner and shop admitted there was more GT3 and it wasn't very cost effective.

They did indeed flop the transmission, and there was diffuiculty fabbing the bellhousing and suspension bits. Also, the GT3 engine needs all the supporting electronics, so in fact the dash instruments were also GT3.

Very cool project tho.

Cool. Which exhaust system did they use?

[blue72s]

Old thread I know but I was just thinking that turning the GT3 gearbox upside down (for Cayman) might not be a bad idea afterall. One of the advantages is that, with the inverted gearbox, the engine location could be lowered, thus lowering the centre of gravity. This should be possible because, unlike the Cayman engine, the GT3 engine doesn’t have a wet sump tank beneath the crankcase so the dry-sump GT3 engine can go further down in the engine-bay until it touches the aero undertray.

Another advantage of inverted gearbox is that it might result better half-shafts angle thus less wear (and less heat) on the bearings of the CV joints.

As you may know, many racing cars run inverted gearboxes for the above mentioned reasons.

Why didn’t Porsche do this with the 914/6 and 916?

Do you agree? Thoughts? Rants?

[petevb]

Originally Posted by blue72s

Old thread I know but I was just thinking that turning the GT3 gearbox upside down (for Cayman) might not be a bad idea afterall. One of the advantages is that, with the inverted gearbox, the engine location could be lowered, thus lowering the centre of gravity. This should be possible because, unlike the Cayman engine, the GT3 engine doesn’t have a wet sump tank beneath the crankcase so the dry-sump GT3 engine can go further down in the engine-bay until it touches the aero undertray.

Another advantage of inverted gearbox is that it might result better half-shafts angle thus less wear (and less heat) on the bearings of the CV joints.

As you may know, many racing cars run inverted gearboxes for the above mentioned reasons.

Why didn’t Porsche do this with the 914/6 and 916?

Do you agree? Thoughts? Rants?

Hmm. The gearbox for the water cooled cars is a weak point and is virtually un-serviceable. The Koni Challenge cars are forced to use it (and the wet-sump motor) for rules reasons, and they go through them with regularity. Far more often than the motor, in fact, which tends to last fairly well under race conditions.

That said, both the X51 motor and trans are cheap- you could replace them a number of times for the cost of the GT3 motor and trans. And the motor does last better than you'd expect under race conditions, and it's lighter than the GT3 motor... So the smart thing is probably to get an X51 3.8l and be happy.

If you can't do that, you might look at a GT3 cup or World Challenge motor (track only- forget emissions). They are true race motors, and the motorsports ECU avoids some of the drive-block and other issues you'd see with a GT3 street motor. Some GT3 Cup years will run fine on pump gas, they are available on the used market, and you can bolt them in without the drive block and other issues. Figure ~410 hp depending on the year, ~$25k-$40k. Also figure ~$25k rebuilds every 80 race hours on a cup motor (actually rebuilt less often than a high strung air cooled motor, and similar to how long a street GT3 motor would last in race conditions). WC spec will add ~40 hp, 10k on the rebuild cost and cut the rebuild time in half.

Cost wise you'd end up so far ahead with the X51 motor that I don't think you could justify the conversion as a one-off. If you were making a conversion "kit" to get the GT3 motor in to the Cayman, and could spread your cost, it might be almost bare-able instead of massively painful.

The lower CG seems possible, but inverting the GT3 gearbox (already designed to put the motor as low as practical) might result in the motor being too low. It's a minor factor in any case- if you've got the extra clearance it's better to leave the motor where it is (even with the under-body) and drop the whole car, IMHO.

-Pete

[blue72s]

Thanks man.

Originally Posted by petevb

Hmm. The gearbox for the water cooled cars is a weak point and is virtually un-serviceable.

AFAIK Porsche is using various gearbox manufacturers for the watercooled cars - Aisin for 997, Getrag for 987S 6-speed, and and I think Aisin or VW for 987 5-speed. Are you saying all of them are un-serviceable?
Is the 987S Getrag still no where near as good as the GT3 Getrag?

it's lighter than the GT3 motor...

By how much?

Some GT3 Cup years will run fine on pump gas, they are available on the used market, and you can bolt them in without the drive block and other issues.

Where is the used market?

When you say 'drive block', do you mean PSM, TC? None of the street GT3 years have PSM but the Mk 3 does have TC.

[petevb]

Originally Posted by blue72s

AFAIK Porsche is using various gearbox manufacturers for the watercooled cars - Aisin for 997, Getrag for 987S 6-speed, and and I think Aisin or VW for 987 5-speed. Are you saying all of them are un-serviceable?
Is the 987S Getrag still no where near as good as the GT3 Getrag?

I don't know the details, but I understand the tools to tear down/ rebuild the 997S gearboxes are not readily available, and they (the synchros especially?) are not nearly as strong as the GT3/ cup/ turbo units. Thus the race teams replace them entirely at significant expense (I've heard as often as every other race weekend under extreme use). This info was current as of a couple years ago, but I believe it's still the case.

By how much (lighter)?

I wish I could answer that better, but I've had a hard time coming by the data. The GT3 street motor is probably ~50 lbs heavier vs the 997 street motor. The GT3 cup motor is lighter than the GT3 street (no variocam, etc). For reference, the dressed 997 street motor lists at 444 lbs, while a 993 motor weighs 511. The GT3 street motor has some lighter components than the 993, but adds variocam and water, and is thus in theory heavier...

Where is the used market?

Race sites- the grand am board, etc. PMNA keeps tabs on motors for sale, but don't tell them you're putting it in a street car. Sometimes the back of Pano or Rennlist...

When you say 'drive block', do you mean PSM, TC? None of the street GT3 years have PSM but the Mk 3 does have TC.

Drive block as in the anti-theft system that insures the engine stays with the car. Can be tricky to defeat.

-Pete